We are currently extending our observations on the immunoregulatory effects of total lymphoid irradiation (TLI), a procedure commonly used for the treatment of human malignant lymphomas. Incompatible bone marrow (BM) allografts can be accepted following pretreatment of recipient mice, rats and dogs with TLI (17 daily fractions of 200 rads), without evoking graft versus host disease (GVHD). During the past year, we have established permanent BM chimerism in parental yields F1 hybrids (C57BL/6 yields (C57BL/6 x BALB/c) F1) with 100% success, and to a lesser degree in complete allogeneic combinations (A/J yields (C57 x BALB) F1) using a modified short TLI protocol consisting of daily fractions of 200 rads each. Short TLI protocols will be further studied in large outbred animals to investigate wether similar regimens could serve as a model for clinical BM and/or organ transplantation. In addition, we have characterized the tumor growth kinetics of the spontaneous, transplantable murine B cell leukemia (BCL1). We will use this animal tumor model to investigate adoptive immunotherapy of leukemia using TLI and allogeneic BM transplantation.